I think Legion means to be a bad guy in the actual main quest. In other words, more than one way to win/finish the main quest. As it is now, there's only one way to do each part of it. Sure, you can be a baddie in terms of guilds and crimes but you can't help overturn the empire, open wide the jaws of Oblivion, and plunge the land into utter darkness.
[shameless plug]Actually, that's one goal of the DemonTide mod I'm working on.[/shameless plug]
...(btw if igis looks at this post happy im using punctuation now?
Thank you very much for the punctuation. Much improved; Much appreciated.